Pierre Antonelli

Using the near infrared VLTI instrument AMBER

AMBER is the General User near infrared focal instrument of the Very Large Telescope Interferometer. Its a single mode, dispersed fringes, three telescopes instrument. A limiting magnitude of the order of H=13 will allow to tackle a fair sample of extra galactic targets. A very high accuracy, in particular in color differential phase and closure phase modes gives good hope for very high dynamic range observation, possibly including hot extra solar planets. The relatively high maximum spectral resolution, up to 10000, will allow some stellar activity observations. Between this extreme goals, AMBER should have a wide range of applications including Young Stellar Objects, Evolved Stars, circumstellar material and many others. This paper tries to introduce AMBER to its future users with information on what it measures, how it is calibrated and hopes to give the readers ideas for applications.

MATISSE: perspective of imaging in the mid-infrared at the VLTI

MATISSE is foreseen as a mid-infrared spectro-interferometer combining the beams of up to four UTs/ATs of the Very Large Telescope Interferometer (VLTI) of the European Southern Observatory. The related science case study demonstrates the enormous capability of a new generation mid-infrared beam combiner. MATISSE will constitute an evolution of the two-beam interferometric instrument MIDI. MIDI is a very successful instrument which offers a perfect combination of spectral and angular resolution. New characteristics present in MATISSE will give access to the mapping and the distribution of the material (typically dust) in the circumstellar environments by using a wide mid-infrared band coverage extended to L, M and N spectral bands. The four beam combination of MATISSE provides an efficient UV-coverage : 6 visibility points are measured in one set and 4 closure phase relations which can provide aperture synthesis images in the mid-infrared spectral regime.

AMBER: the near-infrared focal instrument for the Very Large Telescope Interferometer

AMBER is a focal instrument for the Very Large Telescope Interferometer working in the near infrared from 1.1 to 2.4 micrometers . It has been designed having in mind the General User of interferometric observations and the full range of his possible astrophysical programs. However the three programs used to define the key specifications have been the study of Young Stellar Objects, the study of Active Galactic Nuclei dust tori and broad line regions and the measure of masses and spectra of hot Extra Solar Planets. AMBER combines up to three beams produced by the VLTI 8 m Unit Telescopes equipped with Adaptive Optics and/or by the 1.8 m Auxiliary Telescopes. The fringes are dispersed with resolutions ranging from 35 to 10000. It is optimized for high accuracy single mode measurements of the absolute visibility, of the variation of the visibility and phase with wavelength (differential interferometry) and of phase closure relations with three telescopes. The instrument and its software are designed to allow a highly automated user friendly operation and an easy maintenance.

GI2T/REGAIN interferometer

This paper presents the optical layout of the REGAIN beam combiner including the optical delay line LAROCA with its variable curvature mirror, the field rotator devices, the image and pupil tracking systems and the dedicated visible spectrography. Preliminary studies of foreseen improvements, such as adaptive optics, IR spectrograph and addition of a third telescope, will be discussed.

An interferometric imaging test bench: the densified pupil concept applied to the VLTI

We describe a test bench designed to study the performances of interferometric imaging systems. The main goal is to study the densified pupil concept in the framework of the VLTI. This work is linked to the proposition of a second generation instrument called VIDA (VLTI Imaging with a Densified Array). This bench aims at comparing the imaging performances of the aperture synthesis, Fizeau and densified pupils beam combination schemes and at specifying the technical requirements like cophasing and tip-tilt correction. A Fizeau assembly, using a multi-apertures mask and associated with a wavefront sensor, has been designed. It allows to measure the differential piston between sub-apertures and to link them to the characteristics of the image recovered. A densified assembly is under study by using reflective surfaces or optical fibers to carry the beams and to densify the pupils before the combination.

Design and tests for the correction of atmospheric and instrumental effects on color-differential phase with AMBER/VLTI

The near-infrared instrument AMBER at the VLTI allows, among other interferometric observables, the simultaneous measurement of the phase between various spectral channels. Color-differential phase thus yields spatial and spectral information on unresolved sources, and could lead to such ambitious goals as the spectroscopy of nearby hot, giant exoplanets. This will require, though, an extreme stability on the measurement, which is likely to be affected by chromatic effects at the various stages of the light path. We present how AMBER has been designed to minimize and to calibrate such effects. We give estimates of their contributions from different origins, and present recent measurements of the instrumental stability. We discuss the possibility to supress the residual chromatic effects in post-data treatment in order to reach a precision limited by the photon noise on the differential phase.

APreS-MIDI: aperture synthesis in the mid-infrared with the VLTI

We are studying an optical concept aiming at recombining 4 telescope beams. Interference fringes are sampled in the pupil plane. Such a principle is perfectly adapted for reconstructing images by aperture synthesis at 10 μm with the VLTI. This principle could be used for building a new generation 10 μm instrument, but instead of doing a totally new instrument, we propose the design of an optical module that can supply the current MIDI-VLTI instrument with 4 beams.

AMBER: optical design and expected performance

AMBER, Astronomical Multi BEam combineR, is the near- infrared instrument dedicated to the VLTI. It is presently designed to work with three of either the 8 m or the 1.8 m telescopes from 1 to 2.5 micrometers . Given the expected scientific performance and requirements for AMBER, we derived the functional analysis leading to the present optical configuration using optical fibers to spatially filter the wavefront perturbations, and dispersed fringes. The expected performance is presented in terms of optical quality and sensitivity to misalignments.

Prototype for the European Southern Observatory VLTI fringe sensor

The operation of stellar interferometers suffers from turbulence- induced random fluctuations of optical pathlength difference between collected fields. Active compensation needs an error signal which is provided by a fringe sensor. A phase A study for a fringe sensor for the ESO Very Large Telescope Interferometer (VLTI) has been conducted at OCA, leading to a proposition for the completion of a prototype. In this article, the goals and the principle of the sensor are recalled (see Gay and Rabbia, preceding paper, in this symposium). Its optimal working wavelength is discussed. Results of a numerical simulation of the sensor operation are reported, comprising sensitivity estimates. The proposed setup is then described in the details, emphasis being put on monomode optical fiber related items. Finally, current plans for the testing and the future use of the prototype are outlined.

VLT interferometer upgrade for the 2nd generation of interferometric instruments

ESO is undertaking a large upgrade of the infrastructure on Cerro Paranal in order to integrate the 2nd generation of interferometric instruments Gravity and MATISSE, and increase its performance. This upgrade started mid 2014 with the construction of a service station for the Auxiliary Telescopes and will end with the implementation of the adaptive optics system for the Auxiliary telescope (NAOMI) in 2018. This upgrade has an impact on the infrastructure of the VLTI, as well as its sub-systems and scientific instruments.